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Gold Purity Converter

Converts between karat, millesimal fineness and percentage gold, and shows the hallmark each standard is stamped with.

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In short Karat, fineness and percentage are one number in three dresses: fineness is karat ÷ 24 × 1000, and the percentage is the fineness ÷ 10. So 22 karat is 916.67 fineness and 91.67% gold, 18 karat is exactly 750 and 75%, and 24 karat is the arithmetic ceiling of 1000 rather than a material anyone can actually refine. The stamped hallmark is not always the arithmetic, and the disagreements are the useful part. A hallmark is a GUARANTEED MINIMUM, so it may never round up past what the metal holds — that is why 22K is stamped 916 and not the 917 that ordinary rounding would give. The single exception among the standard marks is 14K, stamped 585 when 14 ÷ 24 is only 583.33: the 585 mark was fixed by European convention first and the karat fitted to it afterwards, so an alloy that is exactly 14 karat does not qualify for the stamp and has to be made slightly richer to earn it. The seven standard marks are 999 for 24K, 916 for 22K, 875 for 21K, 750 for 18K, 585 for 14K, 417 for 10K and 375 for 9K. Finally, karat is not carat. Karat is this ratio out of 24; the carat that gemstones are sold in is a MASS unit of exactly 0.2 grams. A two carat diamond weighs 0.4 g, while a 22 karat chain can weigh anything at all.

How to use the Gold Purity Converter

  1. Enter the purity you have.
  2. Say whether it is karat, fineness or a percentage.
  3. Read the other two, plus the mark that purity is stamped with.

About the Gold Purity Converter

Karat, millesimal fineness, percentage gold and the hallmark stamp for any purity.

What people use it for

  • Reading a hallmark you cannot identify.
  • Converting a karat figure into the fineness a refiner or assay office uses.
  • Checking what a quoted percentage of gold actually means in karat.

Details

The formulafineness = karat ÷ 24 × 1000
22K916.67 fineness, stamped 916
18Kexactly 750 fineness, 75% gold
14K583.33 fineness but stamped 585 — the mark furthest above its own arithmetic
Karat is not caratCarat is a gemstone mass unit of exactly 0.2 g
PrivacyEverything runs in your browser. Nothing you enter is sent anywhere
Fineness is derived from the karat on this page rather than stored, so it cannot disagree with the arithmetic. The hallmark marks are the published external figures, and the three that do not match the arithmetic each say why.

Where this tool stops

Karat, fineness and percentage are definitional and never change. Everything involving money depends on the rate, the charges and the deduction you enter — none of which are stored on this site, because they move constantly. Hallmarking law and the legal minimum karat differ by country; check your national assay office before relying on a stamp.

Explained in our guides

All guides

Frequently asked questions

What is 916 gold?
22 karat. 22 ÷ 24 is 91.666…%, and the hallmark is stamped 916 rather than 917 because a hallmark is a guaranteed minimum and may never round up past the gold actually in the metal. It is the traditional jewellery standard across India, Pakistan, Bangladesh and Sri Lanka, which is why “916” appears on shop signs there.
Is karat the same as carat?
No, and the two are constantly confused because American English often spells both the same way. Karat is a purity RATIO out of 24. Carat is a MASS unit for gemstones, exactly 0.2 grams. A 2 carat diamond weighs 0.4 g; a 22 karat chain has no fixed weight at all.
Why is 14K stamped 585 when 14 ÷ 24 is 583.3?
Because the 585 mark came from European convention before the karat was matched to it, and it is the only standard mark that sits above its own karat. Since a hallmark guarantees a minimum, an alloy that is exactly 14 karat is not entitled to the 585 stamp — it must be made slightly richer than 14K to carry it.
Can gold be purer than 24 karat?
No. 24 karat means 24 parts gold in 24, so it is the definition of pure rather than a limit better refining could beat. In practice even 24K is stamped 999 or 999.9, because refining to an absolute 1000 is not achievable.
Which karat should I buy?
That depends on what the piece has to survive rather than on which number is biggest. 24K is too soft to wear and belongs in bars and coins. 22K suits chains and bangles. 18K is the usual choice where a stone has to stay set. 14K and below are harder and far more scratch-resistant, which is why they dominate everyday jewellery in the United States and Britain.
Are there any usage caps on the Gold Purity Converter?
There is no cost and no cap. The Gold Purity Converter is not a demo of a paid product, so nothing is held back or watermarked.
Can you see what I put into this utility?
No. The Gold Purity Converter runs entirely in your browser using JavaScript. Nothing is transmitted, logged or stored, which you can verify yourself in the Network tab of your browser's developer tools.
Who is the Gold Purity Converter for?
Typical uses: reading a hallmark you cannot identify. Converting a karat figure into the fineness a refiner or assay office uses. Checking what a quoted percentage of gold actually means in karat. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
What are the limits of the Gold Purity Converter?
Karat, fineness and percentage are definitional and never change. Everything involving money depends on the rate, the charges and the deduction you enter — none of which are stored on this site, because they move constantly. Hallmarking law and the legal minimum karat differ by country; check your national assay office before relying on a stamp. Knowing where a tool stops being trustworthy matters more than the cases where it works.
What are the reference figures here?
The formula is fineness = karat ÷ 24 × 1000. 22K is 916.67 fineness, stamped 916. 18K is exactly 750 fineness, 75% gold. These are printed on the page itself, so you do not have to take them on trust.
How precise is the result?
The calculation runs in double precision and the result is shown to ten significant figures, so converting a value and converting it back returns the original. What is displayed is rounded for readability; what is copied is not.

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